A device is described in German Patent Application No. DE 199 61 311, in which the electrical evaluation unit is brought very tightly to the electrical main conductor. This reduces the possibility of coupling in of interference signals. A printed circuit board is soldered to the main conductor with the evaluation unit, between the evaluation unit and the main conductor, via the connecting leads. In order to ensure a good seal against penetrating dampness, this arrangement is extrusion-coated with a plastic material. In this embodiment, it is a disadvantage that first, the expansion coefficients of main conductor and printed circuit board are very different, and consequently, when there are temperature changes and changes in length generated thereby, undesired mechanical stresses may appear between the main conductor and the printed circuit board of the evaluation unit.